Surya Siddhanta
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कोटिकर्णयुताद् बिन्दोर् बिम्बम् तात्कालिकम् लिखेत् । कर्णसूत्रेण दिक्सिद्धिम् प्रथमम् परिकल्पयेत्॥
from the point of intersection of the perpendicular and the hypothenuse describe the moon's disk, according to its dimensions at the given time. Then, by means of the hypothenuse, first make a determination of directions.
english translation
शुक्लम् कर्णेन तद्बिम्बयोगाद् अन्तर्मुखम् नयेत् । शुक्लाग्रयाम्योत्तरयोर् मध्ये मत्स्यौ प्रसाधयेत्॥
And lay off upon the hypothenuse, from the point of its intersection with the disk, in an inward direction, the measure of the illuminated part : between the limit of the illuminated part and the north and south points draw two fish-figures (matsya); -
english translation
तन्मद्ख्यसूत्रसम्योगाद् बिन्दुत्रिस्पृग् लिखेद् धनुः। प्राग्बिम्बम् यादृग् एव स्यात् तादृक् तत्र दिने शशी॥
From the point of intersection of the lines passing through their midst describe an arc touching the three points : as the disk already drawn appears, such is the moon upon that day.
english translation
कोट्या दिक् साधनात् तिर्यक्सूत्रान्ते शृङ्गम् उन्नतम् । दर्शयेद् उन्नताम् कोटिम् कृत्वा चन्द्रस्य साकृतिः॥
After making a determination of directions by means of the perpendicular, point out the elevated (unnata) cusp at the extremity of the cross-line : having made the perpendicular (koti) to be erect (unnata), that is the appearance of the moon.
english translation
कृष्णे षड्भयुतम् सूर्यम् विशोध्येन्दोस् तथासितम् । दद्याद् वामम् भुजम् तत्र पश्चिमम् मण्डलम् विधोः॥
In the dark half-month subtract the longitude of the sun increased by six signs from that of the moon, and calculate, in the same manner as before, her dark part. In this case lay off the base in a reverse direction, and the circle of the moon on the west.
english translation